1. Field of the Invention
The present invention relates to a method of binding vanadium compounds which are formed as reaction products when solid or fluid petroleum residue is burned in vapor generators.
Solid or fluid petroleum residues are formed when crude oil is processed. These residues contain heavy metals in a highly-concentrated form, especially vanadium compounds, but apart from that are suitable for thermal energy exploitation due to their high heating value. When the relatively high heating value of these residues is exploited by combustion in conventionally fired vapor generators, the vanadium leads to high temperature corrosion on heat transfer surfaces, and especially on uncooled supporting parts, when the temperatures thereof are greater than about 540.degree. C. In this temperature range, the vanadium oxide, together with the sodium oxide which is also present in the flue gas, form corrosive chemical compounds, especially the sodium vanadyl vanadates Na.sub.2 O.V.sub.2 O.sub.4.5 V.sub.2 O.sub.5 and 5 Na.sub.2 O.V.sub.2 O.sub.4.11V.sub.2 O.sub.5.
2. Description of the Prior Art
It is known that vanadium can be chemically bound by adding additives such as MgO and other alkaline earths. This results in a reduction of the corrosive vanadium compounds, which melt at relatively low temperatures. The addition of such additives was already tested with the combustion of vanadium-containing oils in large-scale vapor generators, where the vanadium contents of the fuels utilized was less than is the case with the aforementioned petroleum residues which result from the processing of crude oil. For example, with a vanadium content of 141 ppm in a heavy oil, a distinct reduction of the rate of corrosion was measured when the molar ratio of magnesium to vanadium was 5:1.
In order to achieve corresponding effects when the aforementioned petroleum residues are burned, it is necessary, as a result of the considerably greater vanadium content, to also use a correspondingly greater amount of additive in order to bind the vanadium compounds. The quantity of solid material resulting therefrom during combustion of the fluid residues in a vapor generator which is designed for firing heavy oil could not be removed to the extent necessary because the separation system for the solid material does not have an adequate capacity. Another drawback is that the dust contained in the flue gas would discharge large amounts of heavy metals into the atmosphere, thereby greatly polluting the latter.
The conditions are similar for the combustion of solid petroleum residues in conventional vapor generators.
An object of the present invention is to provide a method with which the vanadium constituents which are present in solid or fluid petroleum residues to a large extent lose their corrosive properties when they are burned in vapor generators, and with which the emission values of these constituents are reduced to an environmentally acceptable value.
This object, and other objects and advantages of the present invention, will appear more clearly from the following specification.